It is known that astaxanthin is a kind of red carotenoid and has a strong antioxidant effect.
PTL 1 discloses a method of producing a green alga that produces astaxanthin and a method of producing a green alga containing astaxanthin in a high concentration by irradiating a green alga, the cell of which is changed to a cyst cell, with light under certain conditions.
Green algae belonging to the genus Haematococcus have been known as green algae which accumulate astaxanthin. It has been known that the Haematococcus exists in a state of being grown as a green swarm cell under an appropriate culture and light irradiation conditions and in a state in which the swarm cell is changed to the cyst cell due to stress such as a light environment or nutrition deficiency and a significant amount of astaxanthin is accumulated in the cell.
It is commercially useful to industrially culture a large amount of green algae as raw materials for health food products, pharmaceutical products, or the like. Moreover, a method of increasing the accumulation of astaxanthin in the cyst cell as shown in PTL 1 has been studied.
On the other hand, there is a need to improve the productivity by promoting the growth of the green algae and by shortening the culture period. In this manner, in order to shorten the period required for obtaining a large amount of cells, it is useful to promote the growth of the green algae which is in a state of being the swarm cell, which is a cell prior to being changed to the cyst cell, and to produce a cell in high density in a short period of time. However, the method of promoting the growth of the green algae which is in a state of being the swarm cell is not known.
In addition, a method of growing an organism by promoting photosynthesis using artificial light is known.
For example, NPL 1 discloses an effect of irradiation with red LED light and blue LED light, on the growth of the Haematococcus. 
In addition, PTL 2 discloses a light source for cultivating a plant or the like by simultaneously or alternately turning on the blue LED light and the red LED light.